Back to EveryPatent.com
United States Patent |
5,107,373
|
Jetter
,   et al.
|
April 21, 1992
|
Arrangement for turning image projected on image screen
Abstract
An arrangement for turning an image projected on an image screen has an
image screen, a trapezoidal prism for image turning, and an optical system
for image producing. The prism has an entry surface, a base surface and an
exit surface. The entry surface of the prism encloses with the base
surface an angle which is different from an angle enclosed by the exit
surface of the base surface. A light beam extending on an optical axis of
the optical system for image producing is offset on the exit surface
relative to the optical axis and encloses an angle with the optical axis
which is not equal to zero, and a transmission filter is located between
the prism and the image screen.
Inventors:
|
Jetter; Rainer (Munich, DE);
Schafferus; Eckhard (Puchheim, DE)
|
Assignee:
|
AGFA-Gevaert A G (Leverkusen, DE)
|
Appl. No.:
|
615799 |
Filed:
|
November 16, 1990 |
Foreign Application Priority Data
Current U.S. Class: |
359/833; 353/81; 359/726; 359/737; 359/738; 359/888 |
Intern'l Class: |
G02B 007/18; G02B 005/04; G02B 005/22 |
Field of Search: |
350/445,447,448,286,287,314,6.4
353/81
|
References Cited
U.S. Patent Documents
4529276 | Jul., 1985 | Yamada | 350/445.
|
Primary Examiner: Henry; Jon W.
Attorney, Agent or Firm: Striker; Michael J.
Claims
We claim:
1. An arrangement for turning an image projected on an image screen,
comprising an image screen; a trapezoidal prism for image turning; and an
optical system for image producing, said prism having an entry surface, a
base surface and an exit surface, said entry surface of said prism
enclosing with said base surface an angle which is different from an angle
enclosed by said exit surface of said base surface, a light beam extending
on an optical axis of said optical system for image producing being offset
on said exit surface relative to the optical axis and enclosing an angle
with the optical axis which is not equal to zero; and a transmission
filter located between said prism and said image screen.
2. An arrangement as defined in claim 1, wherein said prism and said
transmission filter are arranged relative to one another in a fixed
relative position and jointly turnable about the optical axis of the
optical system for image producing.
3. An arrangement as defined in claim 2, wherein said prism has an edge
facing toward the optical system for image producing and formed by said
entry surface and said base surface, said edge being flattened
perpendiculary to the optical axis of the optical system.
4. An arragement as defined in claim 3, wherein said optical system for
image producing has an opening, said edge extending into said opening, of
said optical system edge extending into said opening of said optical
system.
5. An arrangement as defined in claim 1, wherein said transmission filter
is formed as a support of a planparallel glass plate arranged
perpendicularly to said optical axis of said optical system.
6. An arrangement as defined in claim 1, wherein said transmission filter
is formed as a tightened transparent foil arranged perpendiculary to said
optical axis of said optical system.
7. An arrangement as defined in claim 1, wherein said tramsmission filter
is arranged directly on said exit surface of said prism.
8. An arrangement as defined in claim 1, wherein said transmission filter
has a density distribution which extends over an exit aperture of said
optical system as considered from said image screen and has a density
course exactly compensating a brightness distribution.
9. An arrangement as defined in claim 1, wherein a relative position of
said prism to said optical system and said angles between said entry
surface and said base surface and between said exit surface of said base
surface of said prism are selected so that a light beam extending along
said optical axis of said optical system has an offset relative to said
axis and leaves said exit surface with an angle relative to said optical
axis that said beam strikes said image screen in a point in which said
optical axis of said optical system intersects a plane of said image
screen.
10. An arrangement as defined in claim 1, wherein said transmission filter
has a circular area with constant transmission <1 and lies in a light path
of a light beam which during exiting from said optical system extends on
said optical axis, said area of said transmission filter is formed so as
to compensate a brightness decrease in an image plane.
11. An arrangement as defined in claim 1, wherein said transmission filter
has an elliptical area with constant trannsmission <1 and lies in a light
path of a light beam which during exiting from said optical system extends
on said optical axis, said area of said transmission filter is formed so
as to compensate a brightness decrease in an image plane.
12. An arrangement as defined in claim 1, wherein said transmission filter
has a circular area with transmission <1 and lies in a light path of a
light beam which during exiting from said optical system extends on said
optical axis, said area of said transmission filter and the distribution
of the transmission within that area are formed so as to compensate a
brightness decrease in an image plane.
13. An arrangement as defined in claim 1, wherein said transmission filter
has an elliptical area with transmission <1 and lies in a light path of a
light beam which during exiting from said optical system extends on said
optical axis, said area of said transmission filter and the distribution
of the transmission within that area are formed so as to compensate a
brightness decrease in an image plane.
Description
BACKGROUND OF THE INVENTION
The present invention relates to arrangement for turning an image projected
on an image screen, by means of a trapezoidal prism for image turning and
an optical system for image producing.
Arrangements of the above mentioned general type are known in the art. One
of such arrangements is disclosed for example in U.S. Pat. No. 4,529,276.
This arrangement includes an optical system for image for producing and a
trapezoidal prism for image turning. A light shield is arranged between
the image producing system and the image turning prism which later on will
be referred to as prism. The main object of the arrangement in accordance
with U.S. Pat. No. 4,529,276 is to reduce the prism without changing the
light density distribution of the projected image. For solving this object
in this patent the prism is simply shortened. Therefore due to the
vignetting of the exit aperture of the projected optical system, the
non-uniform distribution of the light density of the projected image
exiting the prism is compensated by the light shield. The thusly produced
reducing of the prism which directly does not vignet the exit aperture of
the image producing system amounts to approximately 50% in volume and
approximately 25% in the light path. Since the type of glass suitable for
producing of the prism is very expensive and the aberrations of the prism
such as for example astigmatism, distortion and color tranverse error are
proportional to the light path, there is a requirement due to the high
quality requirements with simultaneous cost reduction that the prism be
made as small as possible.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an
arrangement for turning an image projected on an image screen by means of
a trapezoidal prism or image turning in an optical system for image
producing, which is formed so that with smallest possible, cost minimal
prism volume, a reduction of aberrations and uniform light density
distribution in the image plane is achieved and during turning of the
image no image movement occurs.
In keeping with the objects and with others which will become apparent
hereinafter, one feature of the present invention resides, briefly stated,
in an arrangement of the above mentioned general type in which an exit
surface of the prism encloses an angle with base surface of the prism
which is different from an angle enclosed between an exit surface of the
prism and the base surface of the prism, a light beam extending on an
optical axis of the optical system is offset on an exit surface relative
to the optical axis and encloses with the optical axis an angle which is
not equal to zero, and a transmission filter is arranged between the prism
and the image screen.
When the arrangement is designed in accordance with the present invention
it eliminates the disadvantages of the prior art and provides for the
above specified advantages.
Due to combination of the asymmetrical prism, displacement and tilting of
the optical axis and the arrangement of a transmission filter betweeen the
image screen and the pfism is possible:
1. To reduce the prism volume by approximately 60% relative to the prism
used in U.S. Pat. No. 4,529,276 so as to shorten the light path by
approximately 33%;
2. To displace the prism back to the opening plane of the projecting
optical system since no light shield is arranged between them; and
3. To exactly perform any brightness compensation by means of the
transmission filter.
A special advantage is achieved by the asymmetry of the prism, which not
only contributes to the reduction of the prism volume and compensates the
offset of the optical axis of the image producing optical system, but also
is used for compensation of the projection errors.
Thereby the invention provides for the price favorable construction for
turning of an image projected on an image screen with low structural size
and high projecting quality.
The novel features which are considered as characteristic for the invnetion
are set forth in particular in the appended claims. The invention itself,
however, both as to its construction and its method of operation, together
with additional objects and advantages thereof, will be best understood
from the following description of specific embodiments when read in
connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of an arrangement for turning of an image
projected on an image screen, with a trapezoidal prism for image turning
and an optical system for image producing;
FIG. 2 is a view showing an embodiment of a transmission filter used in the
arrangement for image turning;
FIG. 3 is an increased schematic view of the invention arrangement for
image turning without an image screen;
FIG. 4 is an exit aperture of the arrangement for image turning as seen
from the image screen under an image angle of 0.degree.;
FIG. 5 is an exit aperture of the arrangement for image turning as seen
from the image screen under an image angle of 9.degree.;
FIG. 6 is an exit aperture of the arrangement for image turning as seen
from the image screen under an image angle of 15.degree.; and
FIG. 7 is a view substantially corresponding to the view of FIG. 6, but
showing an exit aperture when the arrangement has a filter with an
elliptical area .
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows in principle a construction of an arrangement for image
turning with an object plane 1, an optical system 2 for producing an image
referred hereinbelow as image producing system 2, a trapezoidal prism 3
for turning an image referred to hereinbelow as a prism 3 or an image
turning element 3, an image screen 5 and a transmission filter 4 arranged
between the image screen 5 and the prism 3. An optical axis of the image
producing system 2 is identified with reference numeral 2a. The prism 3
and the transmission filter 4 are arranged in a fixed position relative to
one another and together turnably about the optical axis 2a.
A light beam extending along the optical axis 2a is identified with
reference numeral 1a. After passing the prism 3 it is offset relative to
the optical axis 2a and inclined to the same.
An object point in the object plane 1 which lies not on the optical axis 2a
is identified with reference numeral 1b. A light beam from the object
point 1b to the image screen 5 is identified with reference numeral 1c. An
entry surface of the prism 3 is identified with reference 3a, a base
surface with 3b and an exit surface with 3c. An edge formed by the entry
surface 3a and the base surface 3b extending perpendicular to the optical
axis 2a is flattened and identified with reference numeral 3d.
FIG. 2 shows for example the transmission filter 4 which is composed of a
planparallel glass plate 4a and has a point 4b of maximun blackening at
the location at which the light beam 1a strikes. Instead of one parallel
glass plate 4a, also a transparent foil can be used, which is held by a
not shown foil holder.
FIG. 3 shows an enlarged arrangement for image turning without the image
screen 5, wherein an opening of the image producing system 2 is identified
as 2b. An angle enclosed by the entry surface 3a with the base surface 3b
is identified as .beta..sub.1. An angle which is enclosed by the exit
surface 3c with the base surface 3b is identified as .beta..sub.2. An
angle between the light beam 1a and the optical axis 2a is designated as
.beta..sub.3.
The transmission filter is shown in FIGS. 2-4. It can be formed as a
planparallel glass plate 4a or a tightened foil.
FIG. 4-7 show an outlet aperture 6 of the arrangement for turning the image
with different image angles as seen from the image screen 5. A surface
which is permeable for light from an object in the object plane 1 is
identified with 6a. The image angle in FIG. 4 is 4.degree., in FIG. 5 is
9.degree., and in FIGS. 6 and 7 is 15.degree.. FIG. 7 is a view
substantially corresponding to the view of FIG. 6, but showing an exit
aperture when the arrangement has a filter with an elliptical area.
The operation of the arrangement for turning of an image in FIGS. 1-7 is as
follows:
The light beam 1c from the object point 1b of the object plane 1 is
deviated by the image producing system 2 so that an inverse image of the
object point 1b is produced on the image screen 5. On its way from the
image producing system 2 to the image screen 5 the light beam 1c passes
through the prism 3. It is refracted on the entry surface 3a and the exit
surface 3c and totally reflected on the base surface 3b. Due to the total
reflection on the base surface 3b the image is inverted. In other words,
the object point, for example, 1b, lying underneath the optical axis 2a is
projected by the image producing system and the prism 3 in an image point
located underneath the optical axis 2a. This corresponds to a turning to
the image by 180.degree. relative to an arrangement without the prism 3
for the image turning.
When the prism 3 and the transmission filter 4, as is the inventive
arrangement for image turning, is turnable jointly about an optical axis
2a, the image is turned along during the rotation of the prism 3 and the
transmission filter 4 about the optical axis 2a. Therefore during a
turning of the prism 3 about 180.degree. the image is turned by
360.degree..
Starting from a symmetrical, trapezoidal prism which does not directly
intersect an exit aperture of the image producing optical system 2 and has
a volume, measured in the inventive arrangement, which is greater by the
factor 5, and the light way by the factor 2, the inventive arrangement for
image turning is obtained in five steps:
1. Shortening of the prism 3 in direction of the optical axis 2a. This
feature leads with addition ot the light shield to the arrangement in
accordance with U.S. Pat. No. 4,529,276. In this patent the brightness
compensation by a light shield is performed between the prism 3 and the
image producing system 2.
2. Displacement of the base surface 3b in direction to the optical axis 2a.
Thereby the vignetting produced in the first step is counteracted, whereby
the prism can be further shortened. Image center and turning point no
longer coincide with one another so that during turning the image travels.
3. Flattening of the edge formed by the entry surface 3a and the base
surface 3b so that the thusly produced edge 3b can be displaced to the
opening 2b. This feature leads to the fact that the light beams which
extend not parallel to the optical axis 2a, such as for example the light
beam 1c strike the base surface 3b in the region of the base surface 3b
which lies near on the edge 3d. Thereby a further shortening of the prism
is possible
4. Tilting of the entry surface 3a and the exit surface 3c so that the
angle .beta..sub.1 is not equal to the angle .beta..sub.2. With this
feature the displacement of the optical axis 2a in the second step is
compensated. This means that the light beam 1a strikes the image screen 5
in the point in which the optical axis 2a intersects the image screen 5.
Thereby the image during turning no longer travels. In addition, the image
field is compensated by the proper selection of the angles .beta..sub.1
and .beta..sub.2.
5. Arrangement of a transmission filter 4 directly after the prism 3
between the prism and the image screen 5, which compensates the brightness
reduction.
In this case of a transmission filter 4 from FIG. 2, the point 4b of the
maximum blackening acts so that the surface 6a of the exit aperture 6 as
seen from the image screen 5 remains approximately identical with
different image angles. Thereby an approximately uniform light density
distribution over the projected image is achieved.
In addition to the above described design of the transmission filter 4
further possibilities are provided:
a) Instead of a point of maximum blackening, a point with predetermined
gray value and a surface greater than the surface of the point in FIG. 2
on the planparallel glass plate 4a are brought.
(b) The planparallel glass plate 4a can be evaporated with a continuous
density profile, so that an exact uniform brightness distribution on the
image screen 5 is obtainable.
c) The planparallel glass plate 4a can be replaced by a tightened foil
which has a density course required for brightness compensation.
d) The point of maximum blackening 4b or the point with the predetermined
gray value from the possibility a) of the described arrangement or the
continuous density profile can be brought direcrly on the exit surface 3c
of the prism 3.
During the determination of the geometric parameter of the steps 1-4 and
the transmission filter 4 of the fifth step, the inventive arrangement is
suitable for the image turning to provide higher projecting quality
relative to the prior art with reduced structural size.
It will be understood that each of the elements described above, or two or
more together, may also find a useful application in other types of
constructions differing from the types described above.
While the invention has been illustrated and described as embodied in an
arrangement for turning an image projected on an image screen, it is not
intended to be limited to the details shown, since various modifications
and structural changes may be made without departing in any way from the
spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the gist of
the present invention that others can, by applying current knowledge,
readily adapt it for various applications without omitting features that,
from the standpoint of prior art, fairly constitute essential
characteristics of the generic or specific aspects of this invention.
What is claimed as new and desired to be protected by Letters Patent is set
forth in the appended claims.
Top